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​When it came to animating the hit Disney movie Tangled, the biggest challenge animators had on their hands was hair. Rapunzel, the main character of the movie, was supposed to have 70ft of hair that would weight a total of about 60lbs. There was no way Disney could have animated that much hair to look realistic and be able to do as much as it did in the movie. That's when Dr. Ward, a PhD from UNC Chapel Hill came in. Her speciality? Animating realistic hair.

​Hair simulation is difficult. An average human head has about 100,000 strands of hair. The simulation could reduce that number to about 173 - since hair that's grouped together tends to act one certain way. There are a lot of formulas for a single strand of hair, what its physical parameters are, and how it will react to outside forces.

​Simulations assign these parameters to a whole section of hair, like how much it should weight. Physics-wise, hairs are treated like a math spring system, coded to behave like individual springs. They give a distinct physical property to the hair, one based on Hooke's Law. Certain liberties were taken to insure that the hair would not restrict the character's movements too much, and that the added weight would not debilitate the character. 60lbs is a lot to drag around on your head, after all.

​Dr. Ward set considered all these restrictions, studying clips of real hair to make sure it was perfectly functional in the movie while still being as realistic as possible.